In the United States approximately 500,000 people suffer from inflammatory bowel disease, which can involve either or both the small and large bowel. Ulcerative colitis and Crohn's disease are the best-known forms of inflammatory bowel disease, and both are categorized as “idiopathic” inflammatory bowel disease because the etiology for them is unknown.
Ulcerative colitis involves the colon as a diffuse mucosal disease, characterized by inflammation and ulceration of the mucosa or innermost lining of the colon. This inflammation causes the colon to empty frequently, resulting in diarrhea. Symptoms include loosening of the stool and associated abdominal cramping, fever and weight loss. Although the exact cause of ulcerative colitis is unknown, recent research suggests that the body's natural defenses are operating against proteins in the body which the body thinks are foreign (an “autoimmune reaction”). Perhaps because they resemble bacterial proteins in the gut, these proteins may either instigate or stimulate the inflammatory process that begins to destroy the lining of the colon. As the lining of the colon is destroyed, ulcers form, releasing mucus, pus, and blood. The disease usually begins in the rectal area and may eventually extend through the entire large bowel. Repeated episodes of inflammation lead to thickening of the wall of the intestine and rectum with scar tissue. Death of colon tissue or sepsis may occur with severe disease. The symptoms of ulcerative colitis vary in severity and their onset may be gradual or sudden. Attacks may be provoked by many factors, including respiratory infections or stress.
Although there is currently no cure for ulcerative colitis, treatments are focused on suppressing the abnormal inflammatory process in the colon lining. Treatments including corticosteroids immunosuppressives (e.g., azathioprine, mercaptopurine, and methotrexate) and aminosalicytates are available to treat the disease. However, the long-term use of immunosuppressives such as corticosteroids and azathioprine can result in serious side effects including thinning of bones, cataracts, infection, and liver and bone marrow effects. In the patients in whom current therapies are not successful, surgery is an option. The surgery involves the removal of the entire colon and the rectum.
Crohn's disease can involve any part of the gastrointenstinal tract, but most frequently involves the distal small bowel and colon. Inflammation can produce anything from a small ulcer over a lymphoid follicle to a deep fissuring ulcer to transmural scarring and chronic inflammation. Although the etiology is unknown, infectious and immunologic mechanisms have been proposed. Symptoms are variable and can include diarrhea, fever, and pain, as well as extra-intestinal manifestations of arthritis, uveitis, erythema nodosum, and ankylosing spondylitis.
The traditional approach to treating inflammatory bowel disease is immunosuppression with azathioprine (see, for example, Rutgeerts, J. Gastroenterol. Hepatol. 17(Suppl.):S176–85 (2002)). More recently, the chimeric monoclonal anti-tumor necrosis factor antibody, infliximab, has been used to target specific pathogenic disease mechanisms, and allows thorough suppression of the disease process and healing of the bowel in the long term. However, this therapy is associated with problems of immunogenicity. The formation of antibodies to infliximab interferes with efficacy and is associated with infusion reactions.
Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder. It is a heterogeneous condition characterized by a variety of bowel symptoms including abdominal pain and bloating which are usually associated with altered bowel habit (Collins et al, 2001). It is estimated that between 12 and 20% of the U.S. population suffer from this condition. Differing criteria have been proposed for defining IBS, including the Manning criteria (Manning et al, 1978), the Rome criteria (Thompson et al, 1992), and most recently Rome II (Thompson et al., 1999). Research reports on IBS frequently classify patients with IBS into the two subtypes of constipation predominant (CON) and diarrhea predominant (DIA) and sometimes include a third subtype of alternating pattern (ALT). Prokinetic agents have been a used in treatment of IBS CON for decades. (Callahan, M. J. Clin. Gastroenterol 35 Supp: S58–S67, 2002)
Thus, a need still exists for therapeutic approaches to diagnosis and treatment of inflammatory bowel disease and irritable bowel syndrome.